Combined rectifier and amplifier



A pril28, 193s. K, 6, LACK R.19,943

COMBINED RECTIFIER AND AMPLIFIER CIRCUIT I Original Filed April 25, 19502 Sheets-Sheet 1 61/ a1 'fb .Z 0 ei F I April 28, 1 936. K. c. BLACK19,943

COMBINED RECTIFIER AND AMPLIFIER CIRCUIT Original Filed April 25, 1930 2Sheets-Sheet 2 Reissued Apr. 28, 1936 UNITED STATES PATENT OFFICECOMBINED RECTIFIER AND AMPLIFIER CIRCUIT Knox C. Black,.Mountain Lakes,N. J., assignor, by mesne assignments, to Radio Corporation of America,New York, Delaware N. Y., a corporation of Original No. 1,876,841, datedSeptember 13, 1932, Serial No. 447,303, April 25, 1930. Application forreissue March 2'1, 1933, Serial No. 663,075

16 Claims.

This invention relates to vacuum tube circuits and more particularly tomethods of and circuits for employing a multi-element vacuum tube bothas a demodulator or rectifier of carrier wave signals and as anamplifier for the signal voltage and/ or the rectified voltage.

In accordance with the invention, the external circuits of amulti-element vacuum tube are so arranged that the cathode and anotherelement function as a diode rectifier, and the cathode and two or moreadditional elements function as an amplifier. The amplification mayprecede or may follow the rectification, or reflex circuits may beprovided for amplifying both before and after rectification. The knowncommercial tetrode and pentode tubes having coaxial, cylindricalelements may be employed, but for some circuit arrangement, improvedoperation may be attained when the element acting as the anode for dioderectification is positioned outside of the electron stream establishedbetween the amplifier elements.

Objects of the invention are to provide methods of and circuits foreffecting both amplification and rectification of a signal with a singlemultielement vacuum tube. More particularly, objects are to providemethods of and circuits for employing a multi-element tube for therectification of a signal and for the amplification of the signal atcarrier and/ or audio frequencies.

These and other objects of the invention will be apparent from thefollowing specification, when taken with the accompanying drawings, inwhich,

Fig. 1 is a circuit diagram of one embodiment of the invention.

Figs. 2a. to 20 are fragmentary circuit diagrams illustrating otherembodiments of the invention.

Figs. 3a to Be illustrate forms of coupling devices which could besubstituted in the circut of Fig. 1,

Figs. 4, 5 and 6 illustrate reflex circuits for amplifying both beforeand after diode demodulation of the signal.

Operation in accordance with the present invention is predicated uponthe fact that any tube element in the electron field from a cathodewill, irrespective of the operation of other tube elements, givesatisfactory diode rectification in conjunction with the cathode,provided a small positive direct current voltage will cause appreciablecurrent to flow through the electrode.

As shown diagrammatically in Fig. 1, the vacuum tube may be a pentodehaving three grids serially arranged in the electron field between thecathode C and plate P. The inner grid G acts as a control grid for theamplification of the signal voltage across an input circuit I, the biasbeing provided through resistance 2 by a battery 3. The outer grid G isconnected to the cathode, and the intermediate grid G serves as theanode of a radio frequency amplifier. The amplifier anode circuitincludes a source of current 4 and the primary winding of a. radiofrequency transformer 5.

The amplified radio frequency in the secondary of the transformer 5 isfed through a blocking condenser 6 of low radio frequency impedance tothe plate P of the tube. The plate is also connected through the radiofrequency choke I to the terminal 8 of the audio frequency outputcircuit. The other terminal 9 of the output circuit is connected to thecathode and a radio frequency by-pass condenser Ill and audio frequencyresistance II are shunted across the output terminals 8, 9.

In this circuit, the plate P acts as the anode of an ordinary dioderectifier with parallel feed, i. e., the applied radio frequency voltageswings the plate positive during a part of the cycle and thereby causesrectified current to flow through the resistance l I from the cathode tothe plate. The circuit therefore acts as a combined radio frequencyamplifier and diode detector and, so long as distortionless carrieramplification is afforded by the inner elements, the audio output willbe a linear function of the applied radio frequency carrier amplitudeand degree of modulation within those limits for which the customarydiode causes this linear relation.

The circuit connections for securing both amplification and dioderectification may be varied within wide limits. For convenience ofdescription, the respective upper terminals of the transformer windingsin Fig. 1 are designated as a, b, and the low potential or groundedterminals of the primary and secondary windings are designated as c, d,respectively. The incomplete diagrams, Figs. 2a, 2b and 20, showalternative connections to the vacuum tube. In these views, theterminals a, 27, indicate the points of the network which are to beconnected to that part of the stage network of Fig. 1 which lies to theright of points a, b of that figure. As shown in Fig. 2a., the carriervoltage may be impressed upon the inner grid G the grid G constitutes ascreen grid and the outer grid G is the anode element of the radiofrequency amplifier. In the circuit of Fig. 2b, the grid G is a spacecharge grid, the signal is impressed upon the intermediate grid G andthe grid G is the amplifier anode. The Fig. 2c circuit shows theconnections for a tetrode tube in which the inner grid G constitutes thecontrol grid and the outer grid G is the amplifier anode.

The series of views, Figs. 3a to Sc, show various forms of inductivecoupling that may be employed between the amplifier anode circuit andthe rectifier circuit. Any one of these coupling devices may besubstituted for the transformer shown in Fig. 1 by connecting theterminals a, b, etc., to be correspondingly identified points of theFig. 1 circuit. Fig. 3a shows a transformer coupling in which thedirection of the windings is reversed; Fig. 3b shows an inductiveimpedance coupling; Fig. 3c shows an audio transformer coupling; andFigs. 3d and 3B show transformer couplings including a variablecondenser C for adjusting the coupling circuit to resonance. Resistiveor capacitive couplings may be employed and their design will be obviousto any person familiar with the construction and operation of radiofrequency circuits.

When the performance of an amplifier-detector circuit is investigated,it will be found that the output voltage is a substantially linearfunction of the carrier voltage for signals falling within the range ofvalues for which the amplifier elements act as a distortionlessamplifier. With certain circuit conditions the emission of secondaryelectrons from the plate or diode element of the tube will give anon-linear response but, in general, the limitation of the linear regionis due to overloading of the radio frequency amplifier.

The amplifier detector circuit contemplated by the invention presentsthe possibility of refiexing or feeding the audio voltage back onto theoriginal control grid for further amplification of the signal at audiofrequency. The reflex circuit shown in Fig. 4 employs the generalcircuit arrangement which is shown in Fig. 1 and corresponding elementsof these two views are identified by the same reference numerals.

The transfer of amplified radio frequency voltage from the amplifieranode circuit to the rectifier circuit is effected by a radio frequencychoke 5 that will be recognized as the coupling element shown in Fig.3b. The secondary winding I! of an audio frequency transformer isconnected between the cathode C and the tuned input circuit I, thewinding l2 being shunted by a radio frequency by-pass condenser l3. Theprimary ll of the audio frequency tranformer is connected through acondenser l5 of low audio frequency impedance to a tap l6 that may beadjusted along the resistance Ii, and to the tube cathode. The amplifiedaudio frequency output is made available across the terminals 8', 9' ofa transformer whose primary winding I1 is connected between the radiofrequency choke 5' and the cathode. The operation of this reflex circuitwill be apparent from the above description of the Fig. 1 circuit.

The reflex circuits of Figs. 5 and 6 show possible arrangements in whichtwo tubes operate in parallel for radio frequency amplification anddiode rectification, and in push-pull for audio frequencies. The generalsystem of circuit connections is shown in Fig. 2a, 1. e., the amplifieraction is essentially that of a triode having a screen grid. 7

In the arrangement shown in Fig. 5, the radio frequency input circuitsfor the tubes l8, l9 are substantially identical inductances 20 whichmay be simultaneously tuned to resgnance by the variable condenser 2|and which may be. due to the blocking condensers 22, at different directcurrent or radio frequency potentials. The high potential terminals ofthe inductances 2|] are connected to the control grids G of therespective tubes, and the low potential terminals are connected to thecathode through the radio frequency by-pass condensers 23. I

The inductances 20 are conductively connected to the cathodes throughthe secondary windings 24 of an audio frequency tranformer and the biasbattery 25. The outer grids G constitute the amplifier anode elementsand are connected to the cathodes through radio frequency chokes 26 andthe primary windings 21 of an audio frequency push-pull transformer, thewindings being shunted by radio frequency by-pass condensers 28. Therespective amplifier anodes are connected to the plates P through theradio frequency-condensers 29. the plates P being connected through thecommon radio frequency choke 30 to the audio frequency resistance 3|which is by-passed for radio frequencies by the condenser 32. Thedesired portion of the audio frequency voltage developed in theresistance 3| by the diode rectifier action is impressed, through thetap 33 and audio frequency condenser 34, upon the primary winding 35 ofthe push-pull transformer whose secondary windings 24 are included inthe input circuits of the respective tubes. The Fig. 6 arrangement is asimplified modification of the Fig. 5 circuit which may not be desirablefor all purposes since there is some degeneration due to the fact thatthe audio frequency impedances in the respective input circuits are alsoelements in the amplifier anode circuits of the respective tubes. Thetuned input circuit l impresses the radio frequency signal in parallelupon the control grids G of tubes l8, l9. The general arrangement of theamplifier output circuits and the diode rectifier circuits may besubstantially identical with that shown in Fig. 5, and correspondingelements of the two views will not be described in detail but areidentified by the same reference numerals.

Attention is directed to the fact that, in the Fig. 6 circuit, only thetube l8 acts as a rectifier for the amplified radio frequency output ofboth tube It and tube I9. Tubes l8 and I9 are both shown as pentodes, noconnection being made to the plate P of tube l9, but it is obvious thattube l9 may be a pentode. Tube I8 is preferably of the type described inmy copending application, Ser. No. 446,098, filed April 21, 1930.

The secondary windings 24 of the audio frequency transformer areserially connected between the cathodes of tubes l8, l9, and the lowpotential terminal of the tuned input circuit i. As stated above, thisarrangement of the windings 24 as elements common to the grid and anodecircuits of the amplifier will result in some degeneration, but thissimplified circuit arrangement may be employed where high amplificationis not essential.

Since these reflex circuits demonstrate the possibility of dioderectification and audio frequency amplification with a single tube, itwill be apparent that the impressed radio frequency signal could beapplied directly to the diode rectifier circuit. This use of amulti-element tube as a diode rectifier and audio frequency amplifier isdescribed and claimed in my copending application Serial Number 446,755,filed April 23, 1930.

The method of operation by which radio freouencv amplification isfollowed by diode detection has the special advantage that the operationof the preceding radio frequency amplifier stage is not affected by thediode rectification. The customary method of feeding a diode rectifierdirectly from the preceding amplifier stage is open to the objectionthat the diode, being a power consuming device, loads the input circuitof the amplifier stage and reduces the gain and selectivity. When thediode rectifier is fed, in accordance with this invention, from anadditional amplifier stage comprising elements of the same vacuum tube,greater inherent sensitivity is obtained, due to the amplification inthe amplifierdetector stage, and the gain and selectivity of thepreceding stage are maintained at their normal values.

It will be understood that the specific circuits which are shown in thedrawings are merely illustrative of the invention and that there is awide latitude in the choice of tube constructions and of circuitarrangements for effecting operation in accordance with the spirit of myinvention as set forth in the following claims.

I claim:

1. The combination with a vacuum tube having a cathode, a diode element,a control grid and an amplifier anode, of impedance associated with saidcathode and diode element to constitute a diode rectifier circuit;impedances asso ciated with said cathode, grid and anode to constituteamplifier input and output circuits, and coupling between certain ofsaid impedances to transfer signal energy between said rectifier circuitand one of said amplifier circuits, whereby the signal may be amplifiedand rectified by said vacuum tube, a second tube provided with acathode, diode element, control grid and amplifier anode, and electrodecircuits corresponding to those of the first tube connected to theelectrodes of the second tube.

2. In a combined amplifier-detector stage, the combination with a vacuumtube having a cathode and a plurality of elements, of circuitconnections between one of said elements and said cathode to constitutea diode rectifier, circuit connections cooperating with a plurality ofother elements and said cathode to constitute amplifier input and outputcircuits, and a second tube, having electrodes similar to said firsttube, and electrode circuits corresponding to those of the first tubeconnected to the electrodes of the second tube.

3. A combined radio frequency amplifier-detector stage comprising a tubeprovided with a cathode, plate, control grid and auxiliary coldelectrode, a radio frequency signal circuit connected between thecathode and control grid, a transformer having its primary in theauxiliary electrode circuit, a condenser of low radio frequencyimpedance connected between said plate and transformer secondary to feedthe amplified signal energy in the secondary circuit to said plate, aradio frequency choke and resistor in series connected between thecathode and plate, said plate and cathode providing a diode rectifier ofamplified signals and causing rectified current to flow through saidresistor.

4. A combined radio frequency amplifier-detector stage comprising a tubeprovided with a cathode, plate, control grid and auxiliary coldelectrode, a radio frequency signal circuit connected between thecathode and control grid, a transformer having its primary in theauxiliary electrode circuit, a condenser of low radio frequencyimpedance connected between said plate and transformer secondary to feedthe amplified signal energy in the secondary circuit to said plate, aradio frequency choke and resistor in series connected between thecathode and plate, said plate and cathode providing a diode rectifier ofamplified signals and causing rectified current to fiow through saidresistor, the audio output across said resistor being a linear functionof the amplitude and degree of modulation of the signal energy appliedbetween said control grid and cathode.

5. A combined radio frequency amplifier-detector stage comprising a tubeprovided with a cathode, plate, control grid and auxiliary coldelectrode, a radio frequency signal circuit con nected between thecathode and control grid, a transformer having its primary in theauxiliary electrode circuit, a condenser of low radio frequencyimpedance connected between said plate and transformer secondary to feedthe amplified signal energy in the secondary circuit to said plate, aradio frequency choke and resistor in series connected between thecathode and plate, said plate and cathode providing a diode rectifier ofamplified signals and causing rectified current to fiow through saidresistor, said auxiliary cold electrode being a positive screen griddisposed between the plate and control grid.

6. A combined radio frequency amplifier-detector stage comprising a tubeprovided with a cathode, plate, control grid and auxiliary coldelectrode, a radio frequency signal circuit connected between thecathode and control grid, a transformer having its primary in theauxiliary electrode circuit, a condenser of low radio frenected betweenthe cathode and control grid, a

transformer having its primary in the auxiliary electrode circuit, acondenser of low radio frequency impedance connected between said plateand transformer secondary to feed the amplified signal energy in thesecondary circuit to said plate, a radio frequency choke and resistor inseries connected between the cathode and plate,

said plate and cathode providing a diode rectifier of amplified signalsand causing rectified current to fiow through said resistor, and meansfor tuning said transformer to a desired signal frequency.

8. A combined radio frequency amplifier-detector-audio frequencyamplifier stage comprising a tube provided with a cathode, plate,control grid and at least one auxiliary positive cold electrode, asignal input circuit between the cathode and control grid, a pathbetween the cathode, auxiliary electrode and plate including in series asignal frequency coupling means and a condenser of low impedance tosignal energy, a second path between the cathode and plate including inseries a signal frequency choke and an audio frequency load impedance, apath of low impedance to audio frequency energy connected between saidloadimpedance and the said signal circuit, and means in said first pathadapted to furnish to an audio utilization means amplified audiofrequency energy in the auxiliary cold electrode circuit.

9. A combined radio frequency amplifier-detector-audio frequencyamplifier stage comprising a tube provided with a cathode, plate,control grid and at least one auxiliary positive cold electrode, asignal input circuit between the cathode and control grid, a pathbetween the cathode, auxiliary electrode and plate including in series asignal frequency coupling means and a condenser of low impedance tosignal energy, a second path between the cathode and plate including inseries a signal frequency choke and an audio frequency load impedance, apath of low impedance to audio frequency energy adjustably connectedbetween a point on said load impedance and the said signal circuit, andmeans in said first path adapted to furnish to an audio utilizationmeans amplified audio frequency energy in the auxiliary cold electrodecircuit.

10. A combined radio frequency amplifier-deteeter-audio frequencyamplifier stage comprising a tube provided with a cathode, plate,control grid and at least one auxiliary positive cold electrode, asignal input circuit between the cathode and control grid, a pathbetween the cathode, auxiliary electrode and plate including in seriesa, signal frequency coupling means and a condenser of low impedance tosignal energy, a second path between the cathode and plate including inseries a signal frequency choke and an audio frequency load impedance, apath of low impedance to audio frequency energy connected between saidload impedance and the said signal circuit, and means in said first pathadapted to furnish to an audio utilization means amplified audiofrequency energy in the auxiliary cold electrode circuit, said loadimpedance consisting of a resistor.

11. A a receiver comprising a tube provided with a cathode, a diodeelement, a control grid and an amplifier grid, a source of signal energycoupled to said control grid and cathode, a rectifier circuit betweensaid cathode and diode element, an amplifier circuit coupled to saidcathode, amplifier grid and diode element, and a load circuit includinga resistor coupled to said rectifier circuit, and additional meansincluding an audio frequency transformer for transmitting rectifiedvoltage developed across said resistor to said control grid and cathode.

I i 12. In a signal receiver, av pair of..tubes each provided with acathode, signal grid, plate and auxiliary grid, a radio frequency inputcircuit for the tubes including a common inductance tuned to resonanceby a condenser, the high potential terminal of the inductance beingconnected to the signal grids of the respective tubes, and the lowpotential terminal being connected to the cathode, the inductance beingconnected to the cathodes through the secondary winding of anaudio-frequency input. transformer, the auxiliary grids being the signalamplifier anode elements,

and being connected to the cathodes through radio frequency chokes andthe primary windings of an audio frequency push-pull output transformer, the respective amplifier anodes being connected to the platesthrough radio frequency condensers, a common radio frequency chokeconnecting the plates to an audio frequency load resistance, a desiredportion of the audio frequency voltage developed across the loadresistance being impressed upon the primary winding of the transformerwhose secondary winding is included in the input circuits of therespective tubes.

13. In a signal receiver, a multi-function tube provided with a cathode,a signal grid, an anode and a positive screen grid between the signalgrid and anode, a signal input circuit connected between the cathode andsignal grid, an inductive reactance having a high impedance to signalcurrents connected between the screen grid and cathode, a capacitor oflow impedance to signal currents in series with the anode and saidreactance, and a resistive load arranged, in series between the cathodeand anode of the tube, to be traversed by the space currenttherebetween.

14. In a receiver as defined in claim 13, means connected to saidreactance for tuning the screen grid circuit to the frequency to whichsaid input circuit is tuned.

15. In a receiver as defined in claim 13, an auxiliary grid in said tubeat substantially cathode potential, said auxiliary grid being disposedbetween the screen grid and anode.

16. In a receiver as defined in claim 13, means for maintaining thesignal grid at a substantial negative bias with respect to the cathodewhereby the, signal currents impressed on the control grid are amplifiedin the screen grid circuit.

KNOX C. BLACK.

